jim wrote:
>
>
>>> If you read your engine textbook you will find that the RON
rating is
>>> made under light load conditions just as you describe. You are correct
to
>> No it is not. Apparently you do not know under what conditions the
>> octane ratings are obtained. Contrary to what you said both the Motor
>> method and Research method are obtained at WOT. Do I really need to
list
>> the specifics of methods used?
>
>
> WOT? It's a test engine there is no throttle adjustment per se. The
> engine runs at 600 RPM. Does that sound like WOT? The engine load
> conditions are described as light (according to ASTM) as a result
> it yields a different (higher) octane number than the
> MON test which is not a light load test (again according to ASTM).
> And by the way the test engines that are still used today
> were designed something like 80 years ago - so exactly how much does an
> 80 year old push rod and carb engine tell you about how a modern
> engine will perform with respect to fuel economy. Oh that's right your
> textbook says it doesn't have anything to do with fuel economy . Well
DUH!
>
WOT means wide open throttle which means intake pressure is at
atmospheric. That determines engine load, not the speed of the engine.
Operating conditions for research and motor methods
Research Motor
ASTM D-2699 ASTM D-2700
Inlet T 52 deg C 149 deg C
Inlet Pr Atmospheric <-----WOT!
Humidity 0.0036 -0.0072 kg/kg-dry-air
Coolant T 100 deg C
Speed 600 rpm 900 rpm
Spark 13 deg BTDC 19-26 BTDC
Const varies with CR
A/F Adjust for Max Knock
> The point is motorists don't know what the RON octane number
> is for the fuel in their gas tanks. Or more to the point they don't what
> the octane number is that could be useful when driving for fuel economy,
Thus if
> you change pumps in the interest of getting better fuel economy you have
no idea
> if you are really increasing or decreasing the knock characteristics of
the fuel
> at light load conditions.
>
>
>
>>> The fuels properties to knock under light loads is exactly what the
>>> RON test determines. Engines do knock under light loads even if you
think
>>> they don't ( and even if you can't hear it) and that does impact on
gas
>>> mileage.
Again you confuse speed with load. They are not the same.
>> Interesting assertion here. Please provide a source for this. In my 30
>> years of engine testing this is a new "fact" for me. And in much of my
>> testing, I have acquired and viewed the in-cylinder pressure data and
>> have not seen this.
>
>
>
>
> The RON test is done under light load. It does indeed detect knock
under those
> conditions. How can you claim an engine can't knock under
> light load? The test protocol is all well do***ented.
> What isn't do***ented is the results of that part of the test that would
> actually be useful for increasing fuel economy.
>
The purpose of the test is to determine the fuels susceptibility to
detonation. For this purpose the test is perfectly valid. Sure the speed
is less than that of today's vehicles. Researchers have worked on
developing a "road octane rating" and what they found was that the more
realistic road test method provided results the fell somewhere in
between the RON and MON ratings. This is one of the reasons that things
were simplified to using the pump rating of (RON+MON)/2.
>
>>> The problem is you don't have any idea what the RON rating is
for the
>>> fuel in your gas tank and it can vary quite a lot for any given posted
>>> pump octane rating. But in spite of the fact that you have no idea
what
>>> the octane is in your gas tank under those conditions that could
>>> potentially be giving you better mileage, you are positive it has no
>>> affect on mileage cause you read something in a book.
>
>> This is absurd.
>
> What specifically is absurd? Are you saying it's absurd that I said you
> read a book?
What is absurd is your willingness to disregard the body of published
information on this subject (and there is plenty).
The octane rating of any fuel is only used to rate the propensity of the
fuel to detonate. It does not indicate the heating value of the fuel
itself. This is easy to see. Commercial fuels are sold with octane
ratings of 87 and 93 (pump ratings). Yet both fuels have heating values
within a couple percent of one another. Another example, methanol has
(R+M)/2 = 109, yet has half the heating value per kg as gasoline. The
octane rating does not correlate with the energy in the fuel.
>
> It's not absurd to say that you don't know how octane interacts with
fuel
> mileage in your own car. You have made it clear that for the specific
> types of driving conditions that would lead to fuel economy you don't
know
> what the specific octane characteristics are of the fuel in your car's
> tank. Sure, you may know what the octane characteristics of the fuel are
> when you punch it to pass some guy who is going 65, but that has nothing
> to do with good fuel economy.
>
If the engine does not detonate at a particular operating condition, it
does not matter what the fuel's octane rating is. It was sufficient to
preclude abnormal combustion.
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